In the sector of marine civil construction, the use of auxiliary floating structures or vessels with the aim of carrying out the offshore installation and/or the transport of heavy and/or voluminous structures, for example offshore foundations and wind turbine towers, is known. The large majority of said auxiliary structures consists of large barges or ships with special characteristics intended for these types of operations, the use of which generally entails an extremely high cost, in addition to the fact that they have very little availability, and furthermore they are only able to operate under very specific and favorable weather conditions.
For example, the patent application EP 2597027 A1 describes a system that comprises a floating structure and a working ship, wherein the floating structure comprises a section equipped with a flange so that it can fit in the securing that forms part of said ship. Once the floating structure is connected to the working ship, the installation and maintenance tasks can be carried out. The problem of this invention is that, in addition to the high costs of use and the limited availability of a ship with these characteristics, the floating structure remains fixed by the securing means, making the installation of the same difficult or impossible in certain conditions.
Likewise, the existence of different types of barges with a space intended to accommodate the offshore structure, more specifically the offshore wind turbine tower to be transported and/or installed, is known. The majority of them have a U shape or consist of two parallel structures joined by fixed metal beams, such as that which is described in patent application WO 2010028762 A1. These solutions also have the main problem of the large dimensions thereof and the resulting high costs of the auxiliary floating structures, along with the need for a specific design for each one of them based on the type of wind turbine tower, as is the case, for example, of the barge described in document EP 2905217 A1. Furthermore, these types of solutions are generally associated with elevation or vertical connection elements by means of which the auxiliary floating element supports at least part of the weight of the auxiliary structure. These types of elements, together with the corresponding connection and disconnection processes, reduce the effectiveness and boost the costs of said solutions.
Many of the offshore positioning or transport systems for large structures additionally comprise the use of large extendable vertical metal columns, intended to rest against the sea bed during the installation period, for example the systems described in the patent applications WO 2008071861 A1 and WO 2009153530 A1, which further increases the total cost of said positioning or transport.
On the other hand, the systems described in patent application GB 2501459 A, which are especially designed for the transport and installation of jacket-type offshore platforms, are also known. However, said systems are generally applied to structures that are not self-floating, and therefore they require the use of two auxiliary elements or structures to function, one of them being intended to provide buoyancy to the structure and the other to improve the stability thereof. Likewise, the system described in the aforementioned application comprises a plurality of connection elements (clamps, pre-installed supports, etc.) between the main structure and the auxiliary floating structures, wherein said connection is made in a rigid and secured way, thereby transmitting vertical forces of floating support to the main structure, and as such contributing to the buoyancy thereof. Although this approach is necessary for the transport and installation of non-floating structures (as is the case in GB 2501459 A), it is a drawback for installing self-floating structures, given that it requires the deinstallation or partial removal of the floating system prior to the anchoring of the main structure. This adds complexity and additional steps to the installation methods, thereby affecting working and maintenance times, as well as involving additional costs associated with the same.
Lastly, patent application WO 2014073956 A1 describes a structure for the transport and installation of a fully assembled and erected wind turbine tower, which comprises securing means, an accommodation area and a gate structure. In this case, the auxiliary floating structure is connected and secured to the substructure of the wind turbine. Thus, although the entire assembly can move in a vertical way for the installation and securing of the wind turbine in the definitive position thereof, this solution does not allow for relative movement between the auxiliary floating structure and the wind turbine tower, thereby making the installation operation difficult. Additionally, these types of structures are especially designed for the installation and transport of completely assembled Tension Leg Platform (TLP) wind turbine towers, making the use of them in other types of offshore structures impossible or very difficult.
The present invention is intended to solve the limitations and drawbacks of known systems for the installation and transport of offshore marine structures, by means of a new auxiliary floating system for performing said operations, together with a method associated with said system.